Cone Beam X-ray Luminescence Computed Tomography Based on Bayesian Method

Abstract

X-ray luminescence computed tomography (XLCT), which aims to achieve molecular and functional imaging by X-rays, has recently been proposed as a new imaging modality. Combining the principles of X-ray excitation of luminescence-based probes and optical signal detection, XLCT naturally fuses functional and anatomical images and provides complementary information for a wide range of applications in biomedical research. In order to improve the data acquisition efficiency of previously developed narrow-beam XLCT, a cone beam XLCT (CB-XLCT) mode is adopted here to take advantage of the useful geometric features of cone beam excitation. Practically, a major hurdle in using cone beam X-ray for XLCT is that the inverse problem here is seriously ill-conditioned, hindering us to achieve good image quality. In this paper, we propose a novel Bayesian method to tackle the bottleneck in CB-XLCT reconstruction. The method utilizes a local regularization strategy based on Gaussian Markov random field to mitigate the ill-conditioness of CB-XLCT. An alternating optimization scheme is then used to automatically calculate all the unknown hyperparameters while an iterative coordinate descent algorithm is adopted to reconstruct the image with a voxel-based closed-form solution. Results of numerical simulations and mouse experiments show that the self-adaptive Bayesian method significantly improves the CB-XLCT image quality as compared with conventional methods.

Cone-beam x-ray luminescence computed tomography based on x-ray absorption dosage

“…21 To improve the reconstruction quality of CB-XLCT, Liu et al 20,21 combined a compressive sensing (CS) technique with wavelet transform to improve tomographic images reconstructed from single-view data. Zhang et al 22 further proposed a self-adaptive Bayesian method for CB-XLCT reconstruction and validated its superiority with numerical simulations and mouse experiments.…”

“…[8][9][10][11][12][13] After the first demonstration of XLCT, 1-3 continuous studies have been devoted to improvements of its imaging performance and various XLCT imaging systems have been proposed. [14][15][16][17][18][19][20][21][22] Among them, a narrow-beam XLCT system could provide the highest spatial resolution; however, the imaging time seems incredibly long due to the complicated data acquisition mode. [14][15][16] To reduce the scan time, a cone-beam XLCT (CB-XLCT) imaging system was recently implemented by Chen et al [17][18][19] and then applied to small animal imaging by Liu et al 20 Compared with the narrow-beam XLCT, CB-XLCT could speed up imaging significantly at the cost of spatial resolution.…”

“…Currently, the imaging model of most XLCT systems is based on the assumption that nanophosphors emit light based on the intensity distribution of x-rays within the object, [16][17][18][19][20][21][22] which can be estimated by the Lambert-Beer law. Considering the complicated energy transfer from x-ray photons to electrons and luminescence centers of phosphors, the assumption may not reflect the nature of the x-ray excitation process accurately.…”

Sensitivity study of x-ray luminescence computed tomography

“…Since the discovery, many x-ray imaging methods have been realized, including x-ray computed tomography (CT), which has emerged as one of the most commonly performed medical imaging procedures with over 70,000,000 exams performed annually [1]. The premise behind most x-ray imaging methods, including CT, is that as x-rays penetrate the body, there is modest scattering that occurs which allows for precise localizations of objects deep in tissue [2] and the resulting image contrast formed is due to the differential attenuation of the x-rays. The primary use of CT has been to provide high spatial resolution images of the anatomy.…”

“…Typical x-ray contrast agents are highly concentrated aqueous solutions (typically iodine-based), and thus cannot be employed for molecular imaging due to their high viscosity and limits on osmolality [5]. To further investigate the molecular imaging potentials for x-ray imaging, x-ray luminescence computed tomography (XLCT) has recently been studied and developed by several groups, including ours [2–4, 6–17]. …”